Meters for measuring radio frequency currents have been proposed in the past. It is desirable to measure the current generated in a transmitter-antenna system in order to determine the power dissipated therein to conform with F.C.C. requirements. U.S. Pat. No. 2,134,589 to J. Stanek provides an early teaching of measuring alternating current with the use of a single wound primary passing through a secondary winding. Stanek, however, teaches a circuit which compensates for the impedance of the rectifier placed therein. The present invention, on the other hand, comprises a simple circuit which relies on the characteristic of a current transformer to overcome the effects of rectifying diodes.
U.S. Pat. No. 2,238,298 to H. Wehrlin also teaches a high frequency current measuring device using a single primary winding, a toroidal transformer, and an analog meter. Similarly, Wehrlin does not teach a rectification circuit to provide compensation for temperature variation and the like.
The transmitter-antenna system does not function in a controlled environment. The current metering device should compensate for temperature variation while not introducing additional impedance to the transmitter-antenna system. U.S. Pat. No. 3,914,689 to C. Wright teaches a self-powering temperature compensated rectifier for measuring alternating current which utilizes a first, second, and third diode to compensate for the diode offset voltage. The diode offset voltage is overcome by placing the second compensating diode in opposition with the first diode, the second compensating having current supplied to it by the third diode. This circuit, however, does not function at low signal levels because the offset of the third diode is prevented from supplying current to the compensating diode. The need, therefore, arose for ammeters of a lower full scale range. Therefore, the present invention evolved to provide a different rectifier circuit to accommodate these lower ranges.